Cleaning the bore of a firearm after use is an essential maintenance step to prevent damage to the bore. Ammunition when fired will deposit contaminating material in the bore. If this material is left in place, it can attract moisture and cause corrosion and pitting.
The modern shotgun barrel can be considered to be divided, from breech to muzzle, into four components, i.e., chamber, forcing cone, cylinder and choke. The bore section with the greatest diameter is the chamber, which accepts the shell. For 12, 16, 20 and 28-gauge guns, it has been standardized in the United States at 23/4 inches in length with a slight tapering of diameter from the rear to front. In 12-gauge guns, for example, the chamber diameter at its greatest ranges from 0.800 inch to 0.816 inch, tapering forward to a minimum of about 0.796 inch at the rear portion of the forcing cone. In the forcing cone, the diameter then becomes restricted to about 0.729 inch - the standard diameter of the 12-gauge cylinder (variation in different guns may range from 0.725 inch to 0.735 inch). At the muzzle end of the 12-gauge shotgun barrel, a permanent, adjustable or replaceable choke then diminishes the bore diameter (no decrease for bore cylinder choke) to as small as 0.693 inch for full choke. The choke is the minimum bore diameter.
Shotgun ammunition contains in addition to gun powder and lead or steel shot, plastic packing. All these materials and the by-products of the chemical reaction of burning gun powder can be fused or otherwise deposited in the various parts of the bore. The inaccessibility of these contaminants within the bore coupled with the variations in bore diameter and the stubbornness of these contaminants to solvents and dislodgement presents a cleaning problem that has defeated many attempted solutions.
Prior bore cleaning equipment have utilized rubber backed emerys to dislodge materials from a bore. Carr U.S. Pat. No. #41,481. Metal screening has also been used. Stocking U.S. Pat. No. #3,064,294. Wire brushes have been used, either alone or in combination with absorbent patches of cloth, felt or other materials, for example, those shown in Schnitger U.S. Pat. No. #2,559,376 issued July 3, 1951. The use of wire brushes and other abrasives to dislodge contaminants in the bore is unacceptable for use with many expensive firearms because of the tendency to score or damage the bore.
Absorbent patches have been utilized to carry chemical solvents to inaccessible parts of the bore. The Romaine U.S. Pat. No. #3,205,518 issued Sept. 14, 1965 shows the use of a urethane patch and the Budd U.S. Pat. No. #182,352 shows a cylindrical wool patch. The Carlton U.S. Pat. No. #4,291,477 issued Sept. 29, 1981, shows the use of a spongeous cleaning patch. Patches when used alone are not capable of effectively dislodging fused materials. Patches tend to accumulate contaminants on their surface which act as a barrier to trap solvents within the absorbent body of the patch. If patches are packed within the barrel, their absorbency is reduced even though their ability to dislodge materials is increased. This packed patch configuration is shown in the Brygider U.S. Pat. No. #4,547,924 issued Oct. 22, 1985.
The Kogasaka U.S. Pat. No. #4,497,082 issued Feb. 5, 1985 uses a foamed urethane resin element with net woven cloth in the middle of various shapes. Unless this material is properly supported, it cannot provide proper cleaning properties.